This invention relates to air treatment modules and, more particularly, to protecting a photocatalyst in the air treatment module using a corona discharge device to remove contaminants from the air handling air stream.
Air treatment modules are commonly used in automotive, commercial and residential heating, ventilating, and air conditioning (HVAC) systems to move and purify air. Typically, an air stream flowing through the air treatment module includes trace amounts of contaminants such as biospecies, dust, particles, odors, carbon monoxide, ozone, semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs) such as formaldehyde, acetaldehyde, toluene, propanol, butene, and silicon-containing VOCs.
Typically, a filter and a photocatalyst are used to purify the air stream by removing and/or destroying the contaminants. A typical filter includes a filter media that physically separates contaminants from the air stream. A typical photocatalyst includes a titanium dioxide coated monolith, such as a honeycomb, and an ultraviolet light source. The titanium dioxide operates as a photocatalyst to destroy contaminants when illuminated by ultraviolet light. Photons of the ultraviolet light are absorbed by the titanium dioxide, promoting an electron from the valence band to the conduction band, thus producing a hole in the valence band and adding an electron in the conduction band. The promoted electron reacts with oxygen, and the hole remaining in the valence band reacts with water, forming reactive hydroxyl radicals. When contaminants in the air stream flow through the honeycomb and are adsorbed onto the titanium dioxide coating, the hydroxyl radicals attack and oxidize the contaminants to water, carbon dioxide, and other substances. The ultraviolet light also kills the biospecies in the airflow that are irradiated.
Disadvantageously, typical air treatment module filters have a finite contaminant capacity. Once the contaminant capacity is reached, the filter does not physically separate additional contaminants from the air stream. Contaminants in the air stream may then flow through the filter and become oxidized by the photocatalyst. This is particularly troublesome when the photocatalyst oxidizes silicon-containing VOCs or SVOCs to form a silicon-based glass on the photocatalyst surface. The silicon-based glass may insulate the titanium dioxide from the passing air stream, thereby passivating the titanium dioxide. In severe instances, much of the catalytic activity of the photocatalyst may be lost within two weeks of reaching the contaminant capacity of the filter. To prevent photocatalyst passivation, the filter may be replaced before reaching the contaminant capacity or additional filters may be utilized to physically separate a greater amount of the contaminants, however, the maintenance required to replace a filter in short time intervals or continually monitor a filter may be expensive and inconvenient.
Accordingly, an air treatment module that more effectively protects the photocatalyst from passivating contaminants is needed.